1. Technical Field
The present invention relates to a light emitting device emitting light by electroluminescence and an electronic apparatus having the light emitting device.
2. Related Art
An organic light emitting diode (OLED), that is, an organic electroluminescent (EL) element, is known as a light emitting source small in thickness and weight. The organic EL element has a structure in which at least one organic thin film formed of an organic material is interposed between a pixel electrode and a counter electrode. Current flows in the organic thin film at the same as flowing in both electrodes, whereby the organic film or the organic EL element emits light.
When plural organic EL elements are arranged and the light emission and the light non-emission of each organic EL element are properly controlled, it is possible to display an image having a desired meaning.
Such an organic EL element or an image display device having the organic EL element is disclosed in, for example, JP-A-2001-185354.
In the above-mentioned image display device, it is desirable that the amount of the organic thin film is constant in the respective organic EL elements and is actually in a constant range. Otherwise, the amount of the organic EL material contributing to the emission of light may vary, thereby causing unevenness in brightness. This requirement results in the requirement that when the organic thin film is formed by a liquid droplet ejecting method (ink jet method), the amounts of ejected liquid or ink droplets should be even in the respective organic EL elements.
However, it is usually difficult to solve the above-mentioned problem. This is for various reasons not being completely controlled, such as unevenness in amount of ejected droplets by ejections in the liquid droplet ejecting method (ink jet method) and unevenness in dryness of the respective organic EL elements in the process of drying the ejected liquid or ink droplets.
Such reasons can be removed to some extent by very strictly controlling the manufacturing processes. However, it is needless to say that the limitation in cost exists therein. As a result, it is desirable for preventing the occurrence of unevenness in brightness that the requirement for evenness in amount of the organic thin film all over the organic EL elements and the requirements for simplification and facilitation in manufacturing processes should be accomplished.
A technique of allowing an “EL layer” formed by an ink jet method to extend over “plural pixel electrodes” (see claim 1 of JP-A-2001-185354), and more specifically, a technique of forming the EL layer in a “stripe shape” or “an elliptical or rectangular shape” (see Abstract or FIG. 1 of JP-A-2001-185354), is described in JP-A-2001-185354). Accordingly, in JP-A-2001-185354, it is described that “it is possible to form the EL layer and thus to reduce the processing time by continuously scanning an ink jet head” (see [0010] of JP-A-2001-185354). Therefore, according to the technique disclosed in JP-A-2001-185354, the facilitation in manufacturing processes is accomplished in the meaning.
However, the above-mentioned problem in the drying process may occur. For example, as shown in FIG. 1 of JP-A-2001-185354, when the EL layer is formed in the “stripe shape”, the amount of before-drying material liquid droplets in the longitudinal direction and the lateral direction about one point therein greatly varies (that is, the former is far greater in general). In consideration of a general nature that the liquid or ink droplets are dried from the ends thereof, the unevenness in dryness (evenness in dryness in plural pixel electrodes) can easily occur in this case.
Organic thin films emitting different colors of light, respectively, are formed in the organic EL elements. For example, an organic EL element includes a first organic thin film and an organic EL element adjacent thereto includes a second organic thin film. In this case, for some reasons, the second organic thin film may be mixed into a place where the first organic thin film should be disposed (see [0006] of JP-A-2002-75640). In this case, the mixed organic EL element may not emit light as originally expected. In consideration of this state, the technique disclosed in JP-A-2001-185354 is very disadvantageous. In JP-A-2001-185354, when the above-mentioned event of mixture occurs, the “entire” pixels in a column may not emit light as expected.
This is true in JP-A-2002-75640 and JP-A-2003-208979. JP-A-2002-75640 discloses a technique of forming a “groove” and “allowing an organic EL material to flow in the groove along a nozzle” (see claim 1 and FIG. 2 or 5 in JP-A-2002-75640). JP-A-2003-208979 discloses a technique of ejecting liquid droplets to cells including plural pixels continuously arranged and partitioned by partition walls (see “stripe shape” described and shown in claim 1, [0021], FIG. 1, and claim 2 of JP-A-2003-208979). As can be clearly seen from the above description, JP-A-2002-75640 and JP-A-2003-208979 do not solve the problem described with reference to JP-A-2001-185354.
On the other hand, JP-A-10-151755 discloses an ink jet recording method (Title of the Invention of JP-A-10-151755) of ejecting ink so that the ink ejected in plural scanning operations is arranged in a line with a constant interval (see claim 1, [0010], and [0148] of JP-A-10-151755), so as to accomplish the object of distributing the ink in a line without unevenness, which is described in [0008] of JP-A-10-151755. When this technique is applied to manufacturing the organic EL element or the image display device, the amount of organic thin film in each organic EL element can be made to be in a predetermined range to some extent.
However, it is considered that the technique described in JP-A-10-151755 is on the premise of the “plural scanning operations” and plural scanning operations on the same pixels are required to obtain a satisfactory advantage. Then, the time from the start of process to the end of process is elongated. From this point of view, the contribution of JP-A-10-151755 to the facilitation of manufacture is not great.